Because of their high heat resistance and ozone resistance properties, ethylene/propylene/diene copolymers have been widely used for rubber products such as automotive industrial parts, industrial rubber products, electrical insulating materials, civil engineering and building materials and rubberized fabrics; and plastic blend materials for polypropylene and polystyrene. However, since the ethylene/propylene/diene copolymers are poor in dynamic fatigue resistance, they are not applied to some special uses, for example, rubber vibration insulator, rubber roll, belt, tire, cover materials for vibrating portions, etc.
Natural rubbers are excellent in dynamic fatigue resistance, but they have a problem in practical use because they are low in the heat resistance and the ozone resistance.
With respect to copolymers of higher .alpha.-olefin and non-conjugated diene, U.S. Pat. Nos. 3,933,769, 4,064,335 and 4,340,705 disclose a copolymer of higher .alpha.-olefin, methyl-1,4-hexadiene and .alpha.,.omega.-diene. The methyl-1,4-hexadiene is a mixture of 4-methyl-1,4-hexadiene and 5-methyl-1,4-hexadiene, and these monomers differ in reaction rate from each other. Accordingly, in the case of performing continuous polymerization, it is difficult to recover those monomers for the repeated use. Further, 4-methyl-1,4-hexadiene is different from 5-methyl-1,4-hexadiene in the copolymerization reactivity with the higher .alpha.-olefin, and hence there is such a problem that monomer conversion is low and polymerization efficiency is bad. Moreover, use of .alpha.,.omega.-diene sometimes causes occurrence of gel in the resulting copolymer thereby to give an adverse effect to physical properties of the product finally obtained.
In the processes for preparing the higher .alpha.-olefin copolymer described in the above publications, a titanium trichloride type catalyst or a catalyst formed from titanium tetrachloride and organoaluminum is used, and the catalytic activity is not sufficiently high, resulting in a disadvantage of high production cost.
Vibration-insulating rubber molded products are used for insulating or reducing transmission of vibration, and have been widely used for machines, electric appliances, civil engineering and building materials, automobiles, other vehicles, etc. For these vibration-insulating rubber molded products, natural rubbers and SBR have been mainly used heretofore.
However, the environment wherein the vibration-insulating rubber molded products are used has become more severe in recent years, and there has been requested that the vibration-insulating rubber molded products have long life as well as maintenance-free properties.
In that connection, it is studied to utilize ethylene/propylene/diene type rubbers (EPDM) having excellent thermal aging resistance for the vibration-insulating rubber molded products. However, the vibration-insulating rubber products formed from EPDM have such a problem that fatigue easily takes place under vigorous vibration, so-called under dynamic conditions, and they are easily broken.
Accordingly, there has been eagerly desired the advent of long-life vibration-insulating rubber molded products which are excellent in both thermal aging resistance and dynamic fatigue resistance (flexural fatigue resistance).
The present inventors have earnestly studied to pursue copolymers which are excellent not only in dynamic fatigue resistance (flexural fatigue resistance), weathering resistance, ozone resistance, thermal aging resistance and low-temperature characteristics but also in processability, and to pursue long-life vibration-insulating rubber molded products which are excellent in both of thermal aging resistance and dynamic fatigue resistance (flexural fatigue resistance). As a result, they have found that a higher .alpha.-olefin copolymer which is excellent in the above-mentioned various properties can be obtained by copolymerizing specific higher .alpha.-olefin, specific non-conjugated diene and specific .alpha.,.omega.-diene in the presence of a specific catalyst for olefin polymerization, and accomplished the present invention.